caa a22 4500 463217330 CHVBK 20180405153201.0 cr unu---uuuuu 170326e20070401xx s 000 0 eng 10.1007/s00269-006-0137-3 doi (NATIONALLICENCE)springer-10.1007/s00269-006-0137-3 Low-temperature heat capacities, entropies and enthalpies of Mg2SiO4 polymorphs, and α−β−γ and post-spinel phase relations at high pressure [Elektronische Daten] [M. Akaogi, H. Takayama, H. Kojitani, H. Kawaji, T. Atake] The low-temperature isobaric heat capacities (C p) of β- and γ-Mg2SiO4 were measured at the range of 1.8-304.7K with a thermal relaxation method using the Physical Property Measurement System. The obtained standard entropies (S°298) of β- and γ-Mg2SiO4 are 86.4±0.4 and 82.7±0.5J/molK, respectively. Enthalpies of transitions among α-, β- and γ-Mg2SiO4 were measured by high-temperature drop-solution calorimetry with gas-bubbling technique. The enthalpies of the α−β and β−γ transitions at 298K (ΔH°298) in Mg2SiO4 are 27.2±3.6 and 12.9±3.3kJ/mol, respectively. Calculated α−β and β−γ transition boundaries were generally consistent with those determined by high-pressure experiments within the errors. Combining the measured ΔH°298 and ΔS°298 with selected data of in situ X-ray diffraction experiments at high pressure, the ΔH°298 and ΔS°298 of the α−β and β−γ transitions were optimized. Calculation using the optimized data tightly constrained the α−β and β−γ transition boundaries in the P, T space. The slope of α−β transition boundary is 3.1MPa/K at 13.4GPa and 1,400K, and that of β−γ boundary 5.2MPa/K at 18.7GPa and 1,600K. The post-spinel transition boundary of γ-Mg2SiO4 to MgSiO3 perovskite plus MgO was also calculated, using the optimized data on γ-Mg2SiO4 and available enthalpy and entropy data on MgSiO3 perovskite and MgO. The calculated post-spinel boundary with a Clapeyron slope of −2.6±0.2MPa/K is located at pressure consistent with the 660km discontinuity, considering the error of the thermodynamic data. Springer-Verlag, 2006 Heat capacity nationallicence Entropy nationallicence Enthalpy nationallicence β-Mg2SiO4 nationallicence γ-Mg2SiO4 nationallicence Post-spinel nationallicence Akaogi M. Department of Chemistry, Gakushuin University, Mejiro, Toshima-ku, 171-8588, Tokyo, Japan aut Takayama H. Department of Chemistry, Gakushuin University, Mejiro, Toshima-ku, 171-8588, Tokyo, Japan aut Kojitani H. Department of Chemistry, Gakushuin University, Mejiro, Toshima-ku, 171-8588, Tokyo, Japan aut Kawaji H. Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta-cho, 226-8503, Yokohama, Japan aut Atake T. Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta-cho, 226-8503, Yokohama, Japan aut Physics and Chemistry of Minerals Springer-Verlag 34/3(2007-04-01), 169-183 0342-1791 34:3<169 2007 34 269 https://doi.org/10.1007/s00269-006-0137-3 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00269-006-0137-3 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Akaogi M. Department of Chemistry, Gakushuin University, Mejiro, Toshima-ku, 171-8588, Tokyo, Japan aut NATIONALLICENCE 700 1- Takayama H. Department of Chemistry, Gakushuin University, Mejiro, Toshima-ku, 171-8588, Tokyo, Japan aut NATIONALLICENCE 700 1- Kojitani H. Department of Chemistry, Gakushuin University, Mejiro, Toshima-ku, 171-8588, Tokyo, Japan aut NATIONALLICENCE 700 1- Kawaji H. Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta-cho, 226-8503, Yokohama, Japan aut NATIONALLICENCE 700 1- Atake T. Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta-cho, 226-8503, Yokohama, Japan aut NATIONALLICENCE 773 0- Physics and Chemistry of Minerals Springer-Verlag 34/3(2007-04-01), 169-183 0342-1791 34:3<169 2007 34 269 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer